The Sig Kadet Mk II would also be a great choice, it is an all Balsa built model with Aircraft ply in key locations, such as firewall and wing joiner. the Kadet would not be over powered by your ST 51, would actually fly great with it! I loved my Kadet MkII, still have it, but it's last flight resulted in less than desirable results upon the final take of which resulted in a sudden and unexpected Landing, because it was during a fun fly, and was told that the pattern was going one way, while the prevailing winds at that time were going in the same direction! and even though it would probably only take a few hours to repair, I just never got around to doing the repairs, and that was about 6 years ago..

Craig..